Main fate of low energy photons in matter is photoelectric effect. At intermediate energies, it is Compton scattering (presumably mainly off electrons). At high energies, it is said to be "pair production". Pairs of what? At low energies, mainly electrons and positrons, obviously (neutrino pair production can be expected to have low intensity). But at higher energies? Is photonuclear effect a significant fate of photons compared to pair production, which remains possible at these energies? When the photon has sufficient energy, what is the branching ratio between p(γ,e+e-)p and p(γ,μ+μ-)p? And is a "pair" needed if it is bosons that are generated? For example, do conservation laws allow p(γ,π°)p? Or p(γ,π+)n?